Flexible electronics are mainly divided into flexible elements, flexible displays, flexible sensors and flexible energy sources. Because of their lightness, thinness and flexibility, the flexible electronics have become the trend of development of the next-generation electronic products. The applications of flexible electronics are mainly in the industries of displays, illumination and solar photoelectricity. Among these, illuminating light sources which use organic light-emitting diodes (OLED) have been regarded as the next-generation illuminating light sources. However, to use the OLED illuminations in the industries, the problem of failing to increase the efficiency needs to be urgently solved. Currently, the solution to the problem involves not only the improvement of the light-emitting materials, but also the results of light out-coupling. Calculations made based on the Snell's Law showed that the amount of usable luminance is actually only about 20%. It will be desirable to significantly improve the luminances of OLEDs by the improvements in the external light out-coupling of substrate modes and internal light out-coupling of wavelength and surface plasmon modes.
Accordingly, the lack of improvement in the efficiency of light out-coupling is currently an issue, which needs to be urgently solved.